1. Technical Field
The present disclosure relates to a wavelength division multiplexing passive optical network (WDM-PON) for long-reach transmission using a position adjustment of a broadband light source (BLS). More specifically, the present disclosure relates to a WDM-PON which extends a transmission distance of the WDM-PON by adjusting a position of a BLS so as to procure a high quality of service (QoS) and to reduce transmission costs in an optical network.
2. Discussion of the Related Technology
Demand on a wider bandwidth per each subscriber is increased as voice and text oriented services have evolved to video based services due to a rapid expansion of Internet. To meet this demand, a study on passive optical network (PON) technologies based on optical fiber has actively carried out. The PON technologies are classified as a time division multiplexing passive optical network (TDM-PON) and a WDM-PON.
Generally, a maximum transmission distance between a central office (CO) and each subscriber in a PON is limited to be 20 Km. However, if a long-reach transmission is possible from CO to each subscriber, a region to be serviced by one CO can be increased greatly. For example, when extending the maximum transmission distance of a PON to 60 Km, it is possible to provide services for a certain area by using only one CO, while the same area may be provided with services by using 9 COs when using a PON having a maximum transmission distance of 20 Km. In this case, because signals can be transmitted through optical fibers from a subscriber to CO, a metro network and any equipments for a metro network provided between a subscriber and CO can be removed and thus it is possible to procure a high QoS of signals easily.
Therefore, when using a PON capable of a long-reach transmission, it is possible to reduce the number of CO greatly in a whole optical network. As a result, it is possible to reduce the costs for provision since a large area for installing CO is not required and the number of equipments to be provided for CO decreased. Further, it is possible to enhance QoS of signals provided for a subscriber because information can be possibly transmitted by a single hop from a subscriber to CO.
In addition, in case of a metropolis, it is possible to provide a high quality of services having a wide bandwidth stably by installing a CO at the suburbs of the metropolis without need of installing several COs compactly in a central area thereof and by connecting the installed CO to each subscriber located at an inner area of the metropolis using a PON capable of a long-reach transmission.
Due to the advantages described above, a PON capable of a long-reach transmission may reduce the initial installation costs of an optical network greatly, increase QoS of signals by decreasing the number of hops, and reduce the maintenance costs for maintaining the optical network.
In a TDM-PON having the above advantages, studies on extension of a transmission distance from CO to each subscriber are published in recent articles by D. Nesset, et al., entitled “Demonstration of 100 km Reach Amplified PONs with Upstream Bit-rates of 2.5 Gb/s and 10 Gb/s,” in Proc. of ECOC 2004, paper We2.6.3, 2004 and by Giuseppe Talli, et al., entitled “Feasibility Demonstration of 100 km Reach DWDM Super PON with Upstream Bit Rates of 2.5 Gb/s and 10 Gb/s,” in Proc. Conf. Optic. Fiber Commun. OFC 2005, paper OFI1, March, 2005.
However, it is inevitable to employ an optical amplifier between CO and a subscriber in order to compensate splitting loss in optical power splitters and loss in a long-reach optical fiber used for a TDM-PON. Further, in a TDM-PON, it is required to increase a transmission bit rate to guarantee a high bandwidth per subscriber and therefore a device for compensating dispersion of an optical fiber to accomplish a long-reach transmission. Using an optical amplifier and a device for compensating dispersion results in disadvantages that costs are increased in a PON and reliability of a system is decreased.
FIG. 1 illustrates a view of an exemplary WDM-PON for long-reach transmission. As illustrated in FIG. 1, the exemplary WDM-PON uses, as its light source, wavelength-locked Fabry-Perot Laser Diode (F-P LD) 11a, 11b, 11c, 31a, 31b, and 31c which have been suggested in Korean Registered Patent No. 325687 entitled “A light source for WDM-PON using a wavelength-locked Fabry-Perot laser diode by an injected broadband light source” (hereinafter referred to “'687 Patent”). In case of BLS 13 for upstream signals, loss due to optical fiber 40 positioned between CO 10 and optical network termination (ONT) 30 is inevitably incurred because both BLS 13 for upstream signals and BLS 14 for downstream signals are positioned at CO 10 in the exemplary WDM-PON shown in FIG. 1. The content disclosed in '687 patent is incorporated by reference herein.
As described above, output power of BLS 13 for upstream signals must be increased as a transmission distance is increased, because BLS 13 for upstream signals positioned at CO 10 is injected into F-P LD 31a, 31b, and 31c positioned at ONT 30 after undergoing loss of optical fiber 40. However, there are some disadvantages that the costs for BLS are sharply increased and embodying BLS becomes difficult, as the output power is increased. In addition, it is not easy to handle the high power BLS.
The discussion in this section is to provide general background information, and does not constitute an admission of prior art.